Medical devices generally have a need for improved actuation. While handles with an improved tactile feel have been available, they usually have a one-to-one activation ratio. In such cases, the actuating element of the handle moves the same amount as the working or gripping element of the device. For example, in gastroenterology, a medical device such as a snare may be used to surgically remove polyps from the colon. In such a procedure, it may be necessary for the snare to move from three to eleven centimeters. Moving the actuating element of the handle this same distance, referred to as the “throw” of the instrument, can be very uncomfortable for a surgeon. For those with small hands, handles requiring large throws can be especially difficult to operate, sometimes requiring two hands.
A snare is an electrically conductive loop of wire or cable that operates by electrically cutting and coagulating tissue that needs to be removed from the body. A typical surgical snare comprises an elongated flexible sheath connected at its proximal end to a handle. An elongated flexible cable extends through the sheath, with the proximal end of the cable connected to a movable portion of the handle so that the cable can be retracted and protracted by the surgeon relative to the sheath. An operating loop or snare is connected to the distal end of the cable. A surgeon opens and closes the loop by actuating the movable portion of the handle to protract or retract the cable. When the cable is in its protracted or forward position, the operating loop is outside the sheath and in its fully extended position for snaring, for example, a polyp. A polyp is a pre-cancerous tissue growth in the colon and rectum. As the cable is retracted, the loop is drawn into the sheath and closed.
A snare is inserted through a working channel of an endoscope fitted with a fiber optic camera. In addition to removing polyps, a snare can be used to surgically remove esophageal carcinoma or to perform nephrostomy. To excise a polyp, a doctor first manipulates an endoscope in the tract of the patient until the polyp is located. The end of the snare is extended from an insulating sheath and positioned around the polyp. The snare is then retracted, resecting the polyp. High frequency electrical current, such as radio frequency (RF) current, may be applied to the loop to cauterize the polyp and prevent bleeding.
Attempts have been made to provide a handle with a mechanical advantage that moves only a fraction of the distance of the snare travel. These handles have been complex assemblies with expensive manufacturing costs. In addition, due to friction between the moving parts and the complexity of the assemblies, some of these handles suffer from reduced tactile sensitivity, making it more difficult for the surgeon to operate. Furthermore, some of these handles use an actuating member to drive the cable and snare, while keeping the sheath stationary. Other handles actuate both the sheath and cable in opposite axial directions. This has the effect of pulling the snare into the sheath as the handle is actuated, which may not be appropriate depending on the circumstances. What is needed is a better handle for deploying a snare during endoscopic procedures.